U.S. patent application Ser. No. 267,890 filed May 28, 1981, now U.S. Pat. No. 4,392,620 and entitled Emergency Locking Retractor for a Vehicle Occupant Restraint Belt describes and illustrates two embodiments of the type of emergency locking retractor in which the locking device responds to rapid pull-out of the belt as well as to acceleration of an inertia responsive device. Retractors of this type usually include an inertia wheel that rotates at the same speed as the belt reel when the reel is pulled out relatively slowly but lags behind the belt reel, due to inertia, when the belt is pulled out rapidly. The inertia wheel ordinarily works in conjunction with an inertia spring that maintains a fixed relationship between the positions of the belt reel and the inertia wheel up to some selected rate of change in the velocity of rotation. When the selected rate of change in the velocity of rotation of the reel is exceeded, the rotational inertia of the inertia wheel causes it to lag behind the belt reel. The inertia wheel works in conjunction with a cam wheel that produces axial motion of either the cam wheel or the inertia wheel. The axially movable wheel of the mechanism has locking rachet teeth that engage corresponding complementary ratchet teeth on the side member of a frame of the retractor. A series of ratchet teeth around the circumference of the inertia wheel work with an inertia responsive device, such as a pawl operated by a movable mass that stops rotation of the inertia wheel and causes the cam mechanism to engage the locking ratchet teeth and lock the reel against rotation.
A problem with this type of locking mechanism is that the same change in the relative rotational positions of the inertia wheel and cam wheel that causes the locking mechanism to lock the reel from rotation when the belt is pulled out from the reel can also occur when the belt is being rewound onto the reel and is abruptly stopped in the course of rewinding. In this case, the rotational inertia of the inertia wheel can cause it to run ahead of the cam wheel, thereby causing the same motion of the axially movable wheel toward the side frame of the retractor. Of course, the retractor will not lock, but the locking ratchet teeth on the side member of the frame and on the axially movable wheel come into contact as a result of the inward camming of the axially movable wheel as the inertia wheel runs ahead in rotation of the cam wheel. Over a period of time, repeated contact between the locking ratchet teeth can wear away the tips of the teeth and ultimately reduce the effectiveness of operation of the locking mechanism.